In a large bowl, combine the cubed cooked chicken, chopped celery, halved grapes, and cooked peas.
In a small bowl, whisk together the mayonnaise and Dijon mustard until smooth.
Pour the mayonnaise mixture over the chicken mixture and gently stir until everything is evenly coated; season with salt and pepper to taste.
Cover and refrigerate the chicken salad for at least 1 hour to chill and let flavors meld.
Before serving, fold the sliced almonds into the chilled chicken salad.
Serve the chicken salad on small sandwich bread, rolls, or on a bed of lettuce.
